1. Field of the Invention
The present invention relates to a manufacturing method for a contact hole and, more particularly, to a manufacturing method for a contact hole, which method includes a step for forming a Ti film by employing chemical vapor deposition.
2. Description of the Related Art
Great efforts are being continued for achieving smaller semiconductor devices with higher density. Currently, VLSI semiconductor devices such as memory devices or logic devices designed with a dimensional standard of about 0.15 .mu.m are being developed and their prototypes are being made. With such increasing scale of integration of semiconductor devices, the diameters of contact holes are accordingly being made even smaller; however, it is difficult to reduce the depths of contact holes because of the need for wiring resistance or capacity. For this reason, the aspect ratios of contact holes are rapidly increasing in recent years, and there has been high demand for forming metal electrodes featuring good coverage.
Referring now to FIG. 1, a conventional method for forming a metal film by the chemical vapor deposition will be described. FIG. 1A through FIG. 1C are cross-sectional views illustrative of the steps wherein the ECR plasma chemical vapor deposition is applied to form a barrier metal film on a contact hole.
First, a contact hole 3 is opened on a 1000 nm-thick insulating film 2 on a silicon substrate 1 as illustrated in FIG. 1A. Then, as illustrated in FIG. 1B, a Ti film 5 is formed to a thickness of a few nanometers on the substrate by using an ECR plasma apparatus under a condition wherein the TiCl.sub.4 flow is 24 sccm, the H.sub.2 flow is 30 sccm, the pressure is 0.12 Pa, the microwave power is 2.8 kW, and the film forming temperature is 420 degrees Celsius. In the next step, as shown in FIG. 1C, a TiN film 7 is formed on the substrate in succession by using the same apparatus under a condition wherein the TiCl4 flow is 20 scam, the H.sub.2 flow is 26 sccm, the N2 flow is 6 sccm, the pressure is 0.23 Pa, the microwave power is 2.8 kW, and the film forming temperature is 420 degrees Celsius. In the conventional example, the flow ratio of TiCl.sub.4 to H.sub.2 is controlled to 0.4 or more so as to suppress the spiculate growth of the Ti film, thereby enhancing the flatness of the film surface to improve the step coating property thereof.
In the conventional manufacturing method for a semiconductor device described above, however, the Ti depositing speed depends on the dose of each reactive species rather than the base substrate; therefore, the step coating property of the Ti film heavily depends on the geometrical shape of the substrate. For this reason, a sufficient thickness of the Ti film cannot be obtained at the bottom of the contact hole having a high aspect ratio, so that stable electrical characteristics of a contact electrode cannot be obtained.